Progress 09/15/05 to 09/14/07

Outputs
OUTPUTS: Research accomplishments 2007: (1) Quantified calcium oxalate crystals (COC) levels in leaves of 37 Dieffenbachia cultivars. As indicated in the objective 1 reported 2006, only raphids and druses were found in leaves of the 37 Dieffenbachia cultivars. More druses occurred than raphids regardless of the location in the leaf. The druse densities were 7- to 76-fold greater than those of raphids depending on the cultivar. The density of druses varied from 126 to 481/mm2; while the density of raphids differed from 5 to 45 /mm2 among cultivars. As far as is known, this is the first discovery that abundant druses, rather than raphids occurred in Dieffenbachia leaves. In addition to the wide variation in the COC density among cultivars, two more lines of evidence indicate that COC density is under genetic control. (a) Three pairs of diploid and tetraploid cultivars (diploid cultivars had their chromosomes doubled to be tetraploid cultivars) were included in this study. The COC densities in tetraploid cultivars were at least 34% less than their corresponding diploid cultivars, suggesting that a polyploid approach may be an option for developing cultivars with reduced COC density in Dieffenbachia. (b) Cultivar Star White, a triploid hybrid developed from a cross between 39301 (a hybrid breeding line) and tetraploid Memoria Corsii, had one of the lowest densities of COC, partially due to the fact that Memoria Corsii had low COC density. We also identified a cultivar having a total druse and raphide density of 137/mm2 compared to some cultivars having over 500/mm2. The identified genetic differences in COC densities among cultivars strongly suggest that reduction of COC densities is possible through breeding, which may result in cultivars with less skin irritation. (2) Surveyed 10 other aroid genera to compare similarities and differences of their COC types, quantities, and distribution patterns. These genera were three Aglaonema, one Alocasia, three Anthurium, two Epipremnum, four Homalomena, two Monstera, three Philodendron, three Spathiphyllum, two Syngonium, and one Zamioculcas cultivars. Results suggested the following: (a) only druses and raphids were found in the leaves of these aroids and (b) the density of druses was higher than raphids, which are the similar results found in Dieffenbachia. However, (c) the COC density in the other aroids studied was much lower than that of Dieffenbachia, which may explain why the other aroids had less mammalian toxicity than Dieffenbachia. TARGET AUDIENCES: The target audiences include ornamental foliage plant growers and nurserymen, the ornamental plant industry, and the interior plantscape industry as well as homeowners who use and install foliage plants for interiorscaping. PROJECT MODIFICATIONS: (1) The original project proposed to survey COC of 42 representative Dieffenbachia cultivars. Due to the fast replacement of cultivars in the foliage plant industry, 11 of the 42 cultivars were not readily available in the foliage market, and these cultivars were Bali Hai, Exotic Perfection, Gold Dust, GoldRush, Honey Drew, Leopoldii, Paradise, Snowflake, Tropic Alix, Tropic Breeze, and Tropic Star. In order to have as many cultivars as possible, we included 7 other cultivars: Speckles, Star Bright M-1 (mutant 1), Star Bright M-2, Tropic Forest, Tropic Snow, and Star White M-1 in this study. Thus, a total of 37 Dieffenbachia cultivars were surveyed in this study. (2)The original project proposed to survey nine other aroid genera with at least one cultivar each. We actually used 10 other aroid genera: three Aglaonema, one Alocasia, three Anthurium, two Epipremnum, four Homalomena, two Monstera, three Philodendron, three Spathiphyllum, two Syngonium, and one Zamioculcas cultivars.

Impacts
The density of druses varied from 126 to 481/mm2; and the density of raphids differed from 5 to 45/mm2 among cultivars. This is the first identification of abundant druses, rather than raphids, occurred in Dieffenbachia leaves. This finding may suggest that druses may play an important role as vehicles to carry proteolytic enzymes to mammalian skin. The COC density is under genetic control, and the identified genetic differences among cultivars suggest that reduction of COC densities is possible through traditional breeding using cultivars with low COC density as parents or chromosomal doubling to develop polyploid cultivars. Both approaches could result in cultivars with less skin irritation. Based on the other aroids studied thus far, only raphids and druses occur in leaves of the other aroids, the density of druses was higher than raphids, but the COC density in the aroids studied was much lower than that of Dieffenbachia, which may support the notion that mammalian toxicity of aroids is closely associated with the COC density in leaves.

Publications

• Cao, H., J. Chen, and D.B. McConnell. 2005. Dieffenbachia calcium oxalate crystal formation affected by cultivars, nitrogen rates, light intensity. HortScience 40:1086 (abstract).

Progress 09/15/05 to 09/14/06

Outputs
The objectives are to (1) develop methods of studying the occurrence, type, and distribution of calcium oxalate crystals (COC) in Dieffenbachia; (2) quantify COC levels in leaves and stems of 42 Dieffenbachia cultivars; (3) survey nine other aroid genera to compare similarities and differences of their COC types, quantities, and distribution patterns; (4) evaluate Ca and Mg nutritional programs and light intensity levels on COC formation; and (5) summarize the findings and develop methods of producing less toxic plants. Research accomplishments: (1) Developed methods of studying the occurrence, type, and distribution of COC in Dieffenbachia. The furled leaf, the unfurling leaf, and the first unfurled leaf of D. maculate Carina and Rebecca and D. x Star Bright were excised and placed in 70% ethanol at 60 C for one day, transferred to 95% ethanol at room temperature for 1 hr, washed in distilled water, transferred to 5% NaOH for 1 hr at room temperature, and rinsed three times in distilled water for transection preparation. Transections 5 mm wide were cut from the leaf base, mid-section, and apex. Total counts of raphide and druse idioblasts on several small interveinal areas about 0.4-0.6 square mm on each transection were determined using polarized light microscope equipped with polarizing optics. To prepare for stem sections, the first, second, and third internodes of each cultivar were killed in FAA, soaked in 5% NaOH for 1 hr, placed on glass slides, and gently squashed for observation. Three additional first, second, and third internodes of each cultivars were killed in FAA, dehydrated in TBA, and embedded in Paraplast. Cross and longitudinal sections were cut using a rotary hand microtome. The sections were mounted using Haupt adhesive. All slides were observed under a microscope. The described stem preparation procedures were also used for preparing root and spadix (male, female, and neutral zones) samples of each cultivar. Idioblasts containing raphides and druses were found in stems, leaves, roots, and spadices, and crystal sand in stems. The density of COC raphide idioblasts increased dramatically at sites where lateral roots, buds, or new flowers initiated. Numerous druses were observed in developing leaves, and the ratio of raphides to druses decreased as the leaves and stems matured. The ratios in stems are larger than 1 but less than 0.2 in leaves, indicating that more raphides are in stems and more druses are in leaves. In addition, COC densities varied significantly among the three cultivars. Star Bright has much low density of druses in stem. Carina has consistently lower densities of raphides and druses in stem and lower druses in leaves than Rebecca even though both Carina and Rebecca are sports selected from Camille. (2) A total of 38 Dieffenbachia cultivars and 1 to 3 cultivars of Aglaonema, Alocasia, Anthurium, Epipremnum, Homalomena, Monstera, Philodendron, Spathiphyllum, Syngonium, and Zamioculcas were collected, potted in a soilless medium, and grown in a shaded greenhouse. Investigation on COC type, quantity, and distribution of COC in leaves of these collected plants are in progress

Impacts
This study found that more druses in leaves, which may suggest that it could be druses not raphids that act as vehicles to carry proteolytic enzymes to mammalian skin. This finding could result in the revision of the current concept that raphids play this role. This study also detected that COC quantity is under genetic control as two sports Carina and Rebecca had significantly different levels of COC. Dieffenbachia is an important ornamental foliage plant used worldwide as a living specimen for interior decoration, but it contains some proteolytic enzymes contributing to the irritant effects to mammalian. COC, mainly raphids, have been blamed as vehicles for delivering the enzymes. The identified genetic differences in COC densities among cultivars may suggest that reduction of COC densities is possible through breeding, which may result in cultivars with less skin irritation.

Publications

• Cao, H., J. Chen, and D.B. McConnell. 2005. Dieffenbachia calcium oxalate crystal formation affected by cultivars, nitrogen rates, light intensity. HortScience 40:1086 (abstract)